Conventionally, as the router selecting method, there is the method described in “Virtual Router Redundancy Protocol” (S. Knight, et al.).
In the method described in the literature, a set of routers called virtual routers share one IP address, one router serving as a master router operates as the default router of the LAN, and the other routers are put on standby as backup routers. Priorities are set for the respective routers.
If the master router can no longer operate as the default router of the LAN for some reason, a router having the highest priority among the backup routers starts operating as the master router.
It is possible to improve communication efficiency of the LAN as a whole if the priorities are set in order from the router having the highest packet transfer capability.
However, in this method, there is only one router that can always be used among the virtual routers. It is thus impossible to select an appropriate router for a particular case.
Therefore, it is impossible to select and use a router having an optimum access interface according to the demands of an application. For example, when there is a router with an access interface to a wireless LAN (a wireless LAN router) and a router having an access interface to a cellular network (a cellular router), using the wireless LAN router to perform an FTP requiring a broadband and using the cellular router to operate an IP telephone requiring reliability is impossible.
As a method of solving this problem, for example, there is a method described in JP-T-2003-514442 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application). FIG. 28 is a diagram showing a method described in this published Japanese translation of the PCT patent application. In FIG. 28, in access selection 151, the set access capability given in the information 153 for each router with an interface to each access network concerning that access, and the access capability required by a user which is set in the user preferences 512 of a terminal, are compared, and the terminal determines the optimum router.
However, in the conventional constitution, since the terminal selects a router, there is a problem in that not only routers but also terminals need to have a special function. In general, a communication function of the terminals is low compared with a communication function of the routers. Thus, the addition of this function is unrealistic in terms of cost and apparatus size. In addition, since the terminals select routers individually, there is also a problem in that, if plural terminals select one router, load concentrates on that router and efficient communication cannot be performed.